Think of it this way.

You can have linear setting. Linear is a straight line graph.

You can have exponential setting. Exponential in RC is just like Exponential in math. You can have two different kinds of Exponential settings. You can adjust with a Concave curve or a Convex curve. That being said, you can adjust such that the rate at which the radio responds to input around zero can be adjusted very small or very grate depending on the curve.